Update root element snippet

[kleihan]

The current snippet in Chapter 3.1.3 is as follows:

This snippet shows that element with required namespaces and attributes:

<fixr:repository name="FIX.Latest" version="FIX.Latest_EP284" 
xmlns="http://purl.org/dc/elements/1.1/" 
xmlns:fixr="http://fixprotocol.io/2023/orchestra/repository" 
xmlns:dc="http://purl.org/dc/terms/" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns:xi="http://www.w3.org/2001/XInclude" 
xsi:schemaLocation="https://fixprotocol.io/2023/orchestra/repository repository.xsd">

Clarify that this is an example of how FIX Latest uses Orchestra, change to EP300, change 2023 to 2026. Chapters 3.1.2, 3.1.4 also affected. Same applies to interfaces XML schema (Chapter 4).

Alternative: change to version instead of calendar year, e.g. https://fixprotocol.io/orchestra/v1-1/RC3/...